const a: string = 'foobar'; 
const b: number = 100; // NaN Infinity
const c: boolean = true; // false
const d: null = null;
const e: void = undefined;
const f: undefined = undefined;

const error: string = "100";

// 报错的原因：tsconfig.json中"target": "es5"的配置不能识别到
// ES6中的Symbol、Promise等
const g: symbol = Symbol();
